Bandage face masks.
These are individually packaged for one time use and cost anywhere from $1-$20+ I prefer the cheap ones as I use them mainly on red-eyes and longer flights. They are available at Asian chemists, some duty-free beauty shops during transit or even in the beauty section of some Chinatown/K-town/J-town grocery-department stores.
Olay unscented/sensitive skin foaming face cloths
I always carry a few of these in my carry-on/purse. It really helps me freshen up and remove all the sweat and pollution off my face. Moist wipes usually make me feel as though I just moistened the gunk on my face instead of actually washing it off.
OXY/Stridex acne pads to prevent skin bumps and ingrown hairs. These are the same as the Bliss pads but much cheaper and differently scented. These are also much more gentle than Tendskin.
Lanocreme
I stock up on their body lotion and cream whenever I can. They do wonders for repairing dry travel skin. Sadly they are almost exclusively available in Australia.
Barielle hand and foot cream
These hand/foot creams really last even through harsh soap found in public bathrooms.
Aveda hydrating mask
Extremely soothing for irritated and inflamed skin. This is what I bring with me to sunny destinations.
Anessa (a Shiseido brand available in Asian countries) sheer sunscreen and sunscreen remover.
I have extremely sensitive skin and am very sensitive to most sunscreens. Anessa offers sheer high spf coverage. The sunscreen remover is essential for removing it from the pores. The remover also removes other brands of waterproof sunscreen.
Borghese's Fango mud for trouble spots. My skin tends to yo-yo during travel and at some point I will get a zit or two. A bit of mud on a spot and it helps prevent it from getting any bigger or more irritated. I put this on before bedtime for obvious reasons.
Clinique spot treatment clear gel, if that spot is particularly stubborn and needs to be worked on during the day. Makeup does sit nicely over this if you let it dry first.